Steam is used in many industrial applications such as heating and power conversion. Under some circumstances, steam includes a water vapor phase, which is gaseous water, and a liquid water phase, which is small droplets of water suspended in the water vapor phase. The amount of liquid water phase relative to the water vapor phase is also called the “wetness factor” or “steam quality” and affects performance of steam in some applications.
For example, steam quality affects performance of steam turbine generators. Specifically, turbine blade performance affects steam turbine generator performance. The thermodynamic and aerodynamic performance of turbine blades are determined in part by the surface finish and shape of the blades which can be affected by steam quality. A steam turbine operating in wet steam conditions has lower thermodynamic efficiency then when operating in dry steam. According to “Baumann's Rule,” an increase in steam wetness decreases turbine efficiency. Water droplets from the liquid water phase of steam impact the surface of turbine blades at a high velocity and corrode the blades. Corrosion of turbine blades result in thermodynamic and aerodynamic losses in turbine operation and reduces power output of the steam turbine generator.
Accordingly, it is desirable to be able to measure the quality of steam being used to drive a steam turbine generator as the steam turbine generator is operating. Methods for measuring steam quality exist. One method includes measuring the temperature of wet steam with calorimeters and measuring pressure of the wet steam with pressure gauges. Specific volumes of liquid water and water vapor are determined from steam tables and the steam quality is calculated from those specific volumes.
Therefore, there is a need for an effective and economical apparatus and method for directly measuring steam quality while steam is being used in applications such as in a steam turbine generator.